Vena cava filters are typically used in combination with other thrombolytic agents to treat pulmonary embolism occurring within a patient. These devices are generally implanted within a vessel such as the inferior vena cava, and function by capturing blood clots (emboli) contained in the blood stream before they can reach the lungs and cause permanent damage to the patient. To trap emboli contained within the blood, many conventional vena cava filters utilize a plurality of independent filter legs that can be expanded within the body to form a conical-shaped surface that captures blood clots without disturbing the flow of blood. Once collected, a natural clot lysing process occurs within the body to dissolve the blood clots collected by the filter.
Delivery of the vena cava filter within the body is generally accomplished via an introducer catheter or sheath percutaneously inserted through the femoral (groin) or jugular (neck) veins. Such introducer catheters or sheaths are generally tubular in shape, and include an inner lumen configured to transport the filter in a collapsed position through the body. Once transported to a desired location in the body (e.g. the inferior vena cava), the filter can then be removed from within the catheter or sheath, allowing the filter legs to spring open and engage the vessel wall. A hook, barb or other piercing means disposed on the base of each filter leg can be used to secure the filter to the vessel wall.
The efficacy of vena cava filters is dependent on several factors, including the dimensions of the vena cava, and the alignment of the filter legs when the device is launched within the body. Since many introducer catheters deploy the filter legs simultaneously in a single step, the spring force resulting from the deployment of the filter legs within the vessel may cause the filter to displace from its intended placement position. In some cases, the hooks on the ends of the filter legs may also interfere with each other, causing the filter to asymmetrically deploy within the body.